The MGTX is a multi-center, single-blind, randomized study comparing thymectomy to no thymectomy in non-thymomatous myasthenia gravis (MG) patients receiving prednisone. This NINDS-sponsored project was initiated in September, 2005. The recruitment goal has been 200 subjects -100 to thymectomy plus prednisone and 100 to prednisone alone. This application is for renewal of this grant to extend the recruitment period for an additional two years and complete recruitment by November 2012 and follow patients for three years. The primary outcome and other outcome measures are unchanged from the original protocol. The plan is to continue recruitment and follow-up of all subjects, as randomized, with blinding being maintained until the last enrolled subject has completed all three years of the study. This plan is consistent from the original grant as approved by the study DSMB as well as the investigators, but will now have a longer follow-up for some patients (out to 6 years). For this renewal, we provide below the original specific aims, details of the study design, a study progress report including recruitment results and strategies to enhance recruitment to date, details of the study core components (Clinical Coordinating Center, Data Coordinating Center, and the associated Biomarker in MG study), details of all administrative activities, the baseline demographics of the study population, volume and quality of the data, a timeline for the completion of the study, and an overview of the current MG therapeutic arena and its impact on this study. The only changes we propose from the original study are to reduce the sample size from 200 to 150. The original sample size calculations were inflated to insure adequate sample sizes for anticipated drop-outs and subgroup hypotheses raised by the reviewers. This revision to 150 subjects is based on realistic estimates of our ability to recruit derived from a three-year experience of enrollment and the fact that the 150 total patients (70 additional in this request) remains adequate for our primary specific aim and can be completed within this budget request.